Hydrocephalus is a neurological condition caused by the abnormal accumulation of cerebrospinal fluid (CSF) within the ventricles, or cavities, of the brain. Hydrocephalus, which can affect infants, children and adults, arises when the normal drainage of CSF in the brain is blocked in some way. Such blockage can be caused by a number of factors, including, for example, genetic predisposition, intraventricular or intracranial hemorrhage, infections such as meningitis, or head trauma. Blockage of the flow of CSF consequently creates an imbalance between the rate at which CSF is produced by the ventricular system and the rate at which CSF is absorbed into the bloodstream. This imbalance increases pressure on the brain and causes the ventricles to enlarge. Left untreated, hydrocephalus can result in serious medical conditions, including subdural hematoma, compression of the brain tissue, and impaired blood flow.
Hydrocephalus is most often treated by surgically inserting a shunt system to divert the flow of CSF from the ventricle to another area of the body, such as the right atrium, the peritoneum, or other locations in the body where CSF can be absorbed as part of the circulatory system. Various shunt systems have been developed for the treatment of hydrocephalus. Typically, shunt systems include a ventricular catheter, a shunt valve and a drainage catheter. At one end of the shunt system, the ventricular catheter can have a first end that is inserted through a hole in the skull of a patient, such that the first end resides within the ventricle of a patient, and a second end of the ventricular catheter that is typically coupled to the inlet portion of the shunt valve. The first end of the ventricular catheter can contain multiple holes or pores to allow CSF to enter the shunt system. At the other end of the shunt system, the drainage catheter has a first end that is attached to the outlet portion of the shunt valve and a second end that is configured to allow CSF to exit the shunt system for reabsorption into the bloodstream or inside the peritoneum. In some shunt systems, the shunt valve is palpatable by the physician through the patient's skin after implantation.
Shunt valves, which can have a variety of configurations, can be designed to allow adjustment of their fluid drainage characteristics after implantation. It is generally preferred to enable external adjustment of these characteristics to avoid invasive surgical procedures each time an adjustment is required.
In some shunt systems, the shunt valve contains a magnetized rotor to control the pressure threshold of the valve. Physicians can then use an externally applied adjustment mechanism, such as magnetic programmer, to provide a magnetic field to adjust the pressure threshold of the shunt valve. One issue with magnetically programmable valves is a potential for unintentionally adjusting the valve by the misapplication of an external magnetic field. Unintentional adjustment of the valve could lead to either the overdrainage or underdrainage of CSF, which can result in dangerous conditions, such as subdural hematoma. For example, the direction of physical approach to the valve by a magnetic programmer that includes a powerful permanent magnet, or an inappropriate initial rotational orientation of a magnetic programmer with respect to the valve, has the potential to inadvertently change a setting of the valve.
It is also important to be able to externally read or verify the setting of the valve. With some adjustable valves, x-ray images are used to determine the current setting of the valve, before and after adjustment. With other adjustable valves, the orientation of the rotor in the valve can be read magnetically, using a magnetic compass-like device positioned above the valve, outside the skin of the patient.
Although tools and methods exist for adjusting CSF shunt valve settings, as do other tools and methods for reading a valve setting, a need exists for magnetically programmable valve systems having reduced probability of unintentional adjustment, as well as for tools and methods that provide both adjustment and verification of implantable valve settings.